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Repeated sequences (also known as repetitive elements, repeating units or repeats) are short or long patterns that occur in multiple copies throughout the genome.In many organisms, a significant fraction of the genomic DNA is repetitive, with over two-thirds of the sequence consisting of repetitive elements in humans. [1]
A tract of repetitive DNA in which a motif of a few base pairs is tandemly repeated numerous times (e.g. 5 to 50 times) is referred to as microsatellite DNA. Thus direct repeat tandem sequences are a form of microsattelite DNA. The process of DNA mismatch repair plays a prominent role in the formation of direct trinucleotide repeat expansions. [2]
All tandem repeat arrays are classifiable as satellite DNA, a name originating from the fact that tandem DNA repeats, by nature of repeating the same nucleotide sequences repeatedly, have a unique ratio of the two possible nucleotide base pair combinations, conferring them a specific mass density that allows them to be separated from the rest of the genome with density-based laboratory ...
Interspersed repetitive DNA is found in all eukaryotic genomes. They differ from tandem repeat DNA in that rather than the repeat sequences coming right after one another, they are dispersed throughout the genome and nonadjacent. The sequence that repeats can vary depending on the type of organism, and many other factors.
The name "satellite DNA" refers to the phenomenon that repetitions of a short DNA sequence tend to produce a different frequency of the bases adenine, cytosine, guanine, and thymine, and thus have a different density from bulk DNA such that they form a second or "satellite" band(s) when genomic DNA is separated along a cesium chloride density ...
Highly repetitive DNA consists of short stretches of DNA that are repeated many times in tandem (one after the other). The repeat segments are usually between 2 bp and 10 bp but longer ones are known. Highly repetitive DNA is rare in prokaryotes but common in eukaryotes, especially those with large genomes. It is sometimes called satellite DNA.
DNA strand slippage during replication of an STR locus. Boxes symbolize repetitive DNA units. Arrows indicate the direction in which a new DNA strand (white boxes) is being replicated from the template strand (black boxes). Three situations during DNA replication are depicted. (a) Replication of the STR locus has proceeded without a mutation.
Repetitive DNA sequences comprise approximately 50% of the human genome. [39] About 8% of the human genome consists of tandem DNA arrays or tandem repeats, low complexity repeat sequences that have multiple adjacent copies (e.g. "CAGCAGCAG..."). [40] The tandem sequences may be of variable lengths, from two nucleotides to tens of nucleotides.